It is known in the art, that photographic copying machines use powder-like toner material to copy images. In many machines using toner, a particularly troublesome characteristic is the unanticipated exhaustion of the toner supply. In many of these machines, the toner is kept in a refillable cartridge or chamber into which the powder toner refills are added. When the copier runs out of toner, it must be replenished.
Handling toner material often is unpleasant and troublesome, because it can be dirty and stain anything that it comes into contact with, including clothing, skin, paper and the like. For this reason, determining the toner level in a copier without having to come into contact with it is a desirable feature.
Piezoelectric devices to sense a level of toner material in a copier have been used in the past. A piezoelectric device such as the one shown in FIG. 1, can be made to vibrate at a predetermined frequency, the vibrations of which are dampened or suppressed when the level of powder or toner is such that the powder surrounds or otherwise comes into contact with the piezoelectric vibrating element.
A problem with prior art toner level sensors 2, such as the one shown in FIG. 1, is that false indications are common because the powder material tends to cake up in proximity to the sensor 6. The sensor 6 has relatively wide protective fins 4 around the piezoelectric element 6, which quite often cause the toner material to accumulate on and around the piezoelectric element 6, even though the level of the toner in the copier's canister has dropped by its use.
Since the piezoelectric elements 6 are very sensitive and delicate devices, they are susceptible to damage during installation or other handling. For this reason, fins or veins 4 are provided to protect the piezoelectric elements from damage during both their installation and use over time. The structure and arrangement for these fins has been found to be a source of invalid toner level detection, because of the accumulation of toner material between the fins 4 and the piezoelectric element 6.
A piezoelectric based material sensor that avoids the problems of toner accumulation on or around the piezoelectric element and minimizes false readings, would be an improvement over the art.